The present invention relates generally to fiber optic sensors and, in an embodiment described herein, more particularly provides a method of sensing multiple parameters in a well using a single sensor.
Pressure signals have been measured in subterranean well for many years. These pressure signals may be relatively low frequency, such as pressures monitored during production logging, drill stem testing, well monitoring, etc. These pressures change relatively slowly. Other pressure signals are relatively high frequency, such as pressure signals used in acoustic telemetry, etc., which may have frequencies from many hertz to many kilohertz.
Present sensors used for measuring these pressure signals are typically designed for measuring only low frequency signals or only high frequency signals. If it is desired to measure both low frequency and high frequency signals, then at least two sensors must be used. This circumstance occurs, for example, in operations where acoustic telemetry is used for communication and pressure transducers are used for monitoring well pressure in the same operation.
It would, therefore, be advantageous to be able to use a single sensor to measure multiple parameters, such as low and high frequency pressure signals.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method of sensing multiple parameters is provided which solves the above problem in the art. A fiber optic sensor system is also provided for use in the method.
In one aspect of the invention, a relatively low frequency signal is measured by transmitting light from a light source through a fiber optic sensor. The light is swept over a range of wavelengths. A relatively high frequency signal is also measured by transmitting light from the light source through the sensor at a constant wavelength.
In another aspect of the invention, the light source is a tunable laser and the fiber optic sensor is an interferometric sensor, for example, using a Mach-Zehnder or Michelson interferometer. The sensor has two optical paths. One of the optical paths changes in length in response to a change in a signal, such as pressure, applied to the sensor.
In a further aspect of the invention, an optical output of the sensor is input to a computer via an opto-electric converter. The computer controls the wavelength output of the light source.
In yet another aspect of the invention, multiple sensors may be connected to the light source to measure signals at each of the sensors.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings.